It is known from the prior art to use epoxy glue to affix a ball lens of an optical submount. Usage of epoxy glue has several disadvantages:                the epoxy glue is aging and has a poor long term reliability,        the stability of the epoxy glue is strongly decreasing at high temperatures,        the process of gluing a ball lens by means of epoxy glue is both time consuming and expensive as it is difficult to apply a tiny quantity of epoxy glue below the ball lens,        the position of the ball lens is defined with a greater tolerance in comparison to the tolerance which is achievable by anorganic attachment. This is because a substantial quantity of epoxy glue is required for gluing the ball lens which creates a greater tolerance with respect to the exact position.        
As far as anorganic attachment is concerned it is as such known from the prior art to utilize an aluminiumaluminium-oxide bonding process:
U.S. Pat. No. 5,178,319 shows compression bonding method for permanently bonding elements such as glass spheres and optical fibers to aluminium surfaces of substrates by applying pressure along with energy to the interface of the element and the aluminium. For example, a glass sphere is bonded by pressing it against aluminium while heating the aluminium. As an alternative to heating, acoustic energy can be applied to the sphere along with the pressure. Glass optical fibers can be bonded to aluminium surfaces in the same manner. The publication “AlO bonding: a method of joining oxide optical components to Al coated substrates”, Coucoulas at el 1993, IEEE conference proceedings, shows a similar method.
This process requires that an aluminium layer is deposited in a processing step when the substrate is structured. Thus the aluminium layer is exposed to several aggressive processing steps such as exposure to acids, reflow at temperatures around 300° C., etc. Such processing steps deteriorate the quality of the aluminium surface. This is a substantial problem as the aluminium-oxide bonding technique requires a contact between oxide, such as SiO2, and pure non-oxidized aluminium. As a consequence the quality of the aluminium-oxide bond formed between the ball lens and the substrate is decreased because of such processing steps to which the aluminium layer is subjected.
U.S. Pat. No. 5,124,281 describes a method of making a V-groove such that a spherical lens can be precisely located within it: A laser is mounted on a planar surface of a monocrystalline silicon mounting member. A spherical lens is mounted in a monocrystalline silicon cover member which, when abutted and registered to the mounting member, aligns the spherical lens with the laser so that the output light can be projected along a precise predetermined path.
The spherical lens is mounted in a V-shaped groove which is made in the cover member by masking and etching. A second V-shaped groove intersects the first groove and defines a V-shaped edge in one side of the first groove. The spherical lens is then seated in the first V-shaped groove such that it bears against two points of the V-shaped edge and against one side wall of the first V-shaped groove. A second lens is mounted in the cover member in the same manner as the first lens and directs laser light from a rear facet of the laser to a mirror 30 and hence to a photodetector mounted in the cover member.
From U.S. Pat. No. 5,933,707 a further method for crystal substrate processing is known. An anisotropic silicon etchant is used in a processing stage to form precision machined features in the substrate. Prior to the use of the etchant a masked layer of organic dielectric is applied to the substrate. The dielectric protects surface features previously defined. By etching the I/Os in the final passivation prior to the deposition of solder, the application of the organic dielectric protective layer and the etching of the V-grooves, the etchant is prevented from accessing the opened I/Os and the number and complexity of the patterning stages is thereby reduced.